if the billing rate for running something is a delta (like you posted, 0.01/second) of time, then having a timer (or cron, or batch, or kafka, whatever) that re

if the billing rate for running something is a delta (like you posted, 0.01/second) of time, then having a timer (or cron, or batch, or kafka, whatever) that records the usage is also atomically deducting it from the account_balance. The account_balance is then topped up with whatever payment schema you want to create. The main issue is that you track the usage as a variable of a constant value to deduct from the account_balance variable of a constant value. Your design is sound. Multiple rates against a running balance, that running balance's constant value is, well, USD. So the rate of usage is USD. Credits/Debits table is really there for reporting and has no bearing on the running_balance. Good luck!